The present invention relates to multiple-stage gas separation in a submersible pump system for producing hydrocarbons from gassy wells. More particularly, the present invention relates to a method and apparatus for modifying and combining a plurality of commercially available single-stage gas separators into a high-efficiency multiple-stage gas separator for protecting a submersible pump system from gas lock.
Submersible pumps carried on the lower end of production tubing provide an economically attractive means to produce hydrocarbons under a variety of circumstances. However, such submersible pumps are susceptible to vapor or gas lock in environments having a high gas-liquid ratio. Gas lock is a type of pump failure brought on by an influx into the pump of substantially compressible fluids, i.e., the gaseous components of the production fluid. Once seized in gas lock, it may be difficult to circulate the gaseous component out of the pump to resume normal function. At best, this requires cessation of production to cycle the submersible pump. At worst, gas locking can result in failure of the submersible pump system requiring a trip of the production tubing to access the pump system. The trauma of gas lock stresses the components of the submersible pump and contributes to excessive wear and premature failure of both the pump and the motor, especially in combination with the excessive motor temperatures generated during gas locking. It does not take many preventable trips of the production tubing out of well bore to service a submersible pump or motor in order to substantially alter the economic considerations which otherwise favor submersible pump systems over alternatives for a specific application.
In the past, a single-stage gas separator has been deployed upstream of the pump in order to extend the range of submersible pump systems to formations having a gaseous component of the production fluids. While single-stage gas separators are helpful in limited ranges, gas lock continued to be a substantially limiting factor in the deployment of submersible pumps for production from gassy wells.
Applicants' co-pending application addresses a method and apparatus for high efficiency gas separation in which a submersible pump system operating in a high gas-liquid ratio well is protected from gas lock with multiple-stage gas separation which effectively separates the gaseous components of the produced hydrocarbons upstream of the pump and passes these gaseous components to the annulus between the production tubing and the casing. Thus, the fluid advancing to the submersible pump is substantially limited to the liquid components of the production fluid. However, establishing multiple-stage gas separation upstream of the pump in the severe dmensional constraints of the bore hole is a formidable problem. Further, it would be desirable to provide for combination of a plurality of existing single-stage gas separators into a multiple-stage gas separation as a method to provide an economical, immediate solution into practice, but conventional single-stage gas separators are not compatible for such combination.